Light transport through Mie resonances in Photonic Glasses

The authors present a novel photonic material dubbed photonic glass, which is a solid, disordered, macroscopic assembly of monodisperse dielectric spheres. These spheres, whose diameter is of the order of the wavelength of the light, support Mie resonances and, as a result of a collective effect of these resonances, the photonic glass is expected to exhibit a resonant behaviour in the diffusion constant and in the transport mean free path. We report the first measurement of these macroscopic resonances, as well as the frequency dependence of the energy velocity of the diffuse light, which decreases below the group velocity when Mie resonances are excited. From total diffuse transmission measurements we can derive the transport mean free path and show the presence of diffusive modes at different frequencies, with different transport properties. From time-resolved measurements of the spreading of a short pulse travelling through the sample, and of its exponential tail, we can extract the resonant values of the diffusion constant.